London Metropolitan police said Tuesday that the claim was made one day earlier to a media outlet in Northern Ireland “using a recognized codeword.”

“Given the packages received last week bore similarities to devices sent in the past which were linked to dissident groups associated with Northern Ireland-related terrorism, officers were already looking at this as a line of enquiry,” police said in a statement. “However, we continue to keep an open mind and enquiries continue.”

The group took responsibility for five package bombs, according to police and The Irish News. By Tuesday, police said they had recovered four of the devices – three in London and one in Scotland.

The discovery of the first three devices near transportation hubs in London caused major disruptions March 5. The first package was found at The Compass Center near Heathrow Airport, where it was partially opened by staff members. Police said the device sparked and caught fire, but no injuries were reported.

Two other devices were subsequently found in the mailroom at Waterloo Station, a major rail and London Underground hub, and at the offices of City Aviation House, near London’s City Airport. Neither package was opened, and no injuries were reported.

A fourth suspicious package was found March 6 at the University of Glasgow, according to police. Authorities evacuated several buildings as they investigated the device, which was subsequently destroyed in a controlled explosion.

The News reported that the package sent to Scotland had been “intended for a British army recruitment officer who works there.” The group taking responsibility for the devices claimed a fifth, undiscovered device was also addressed to a recruitment officer.

The group is the latest incarnation of the Provisional Irish Republican Army, which waged a bloody, decades-long paramilitary campaign in opposition to British rule in Northern Ireland, according to the Independent and Reuters.

The group, sometimes called the “New IRA,” is much smaller than the Provisional IRA had been, according to Reuters. The group claimed to have sent explosive devices in February 2014 to seven military recruitment offices in southeast England, the News reported. The group was also suspected of a January car bombing in Derry, according to the Independent.